Tandem solid-hybrid rocket motor

ABSTRACT

A single-chamber rocket motor containing both a hybrid fuel charge (with associated oxidizer) and a solid propellant charge. Termination of the hybrid motor at the time desired provides accurate missile range zoning. The hybrid fuel charge is in tandem with and forward of the solid propellant charge which provides the minimum impulse of the rocket motor and the minimum missile range. The volume vacated by the solid propellant charge serves as a mixing chamber for more efficient hybrid fuel charge combustion. A gas mixer baffle plate separates the two charges and provides additional mixing.

DU'LDLO umwu mates Patent 1 1 3,789,610 Stone Feb. 5, 1974 TANDEMSOLID-HYBRID ROCKET MOTOR 3,136,] 19 6/1964 Avery /251 Inventor: WilliamC. Stone, Huntsville, Ala.

Przmary Examiner-Samuel Femberg Asslgneei The Unlted States of Americaas Attorney, Agent, or F irm-Edward J. Kelly; Herbert represented by theSecretary of the Ber] Army, Washington, DC.

[22] Filed: June 21, 1967 [57] ABSTRACT [21] Appl. No.: 649,420 Asingle-chamber rocket motor containing both a hybrid fuel charge (withassociated oxidizer) and a solid 52 US. Cl. 60/245, 60/251 F P Telmmatonthe time desired provides accurate missile range zon- [51] Int. Cl. F02k3/00 in The h brid fuel char 6 is in tandem with and 58 Field of Search60/207, 220, 224, 225, 250, Y g

60/251 245 ward of the Solid propellant charge which provides theminimum impulse of the rocket motor and the mini- [561 References Citedfilfiefllfii ihilli S32 2? $1355; 62113112 11? UNITED STATES PATENTSmore efficient hybrid fuel charge combustion. A gas 2,71 1,630 6/1955Lehman 60/250 mixer baffle plate separates the two charges and pro- 3,lCohen et al. vides additional 3,040,5 l7 6/1962 Ryden et al 60/2253,128,599 4/1964 Carr 60/251 9 Claims, 4 Drawing Figures TANDEMSOLID-HYBRID ROCKET MOTOR BACKGROUND OF THE INVENTION This inventionrelates to a novel apparatus for missile range zoning for use in smallmissiles, and in particular to such an apparatus for use in artilleryrockets.

Range zoning for artillery rockets using solid propel lant rocket motorshas been obtained in the past by variations in firing elevation and/ormotor thrust termination. However, the high-altitude flights necessaryfor short ranges induce wind drift errors, while severe thrust peaksusually result when solid propellant motors are terminated. Accordingly,an apparatus for motor thrust termination which can be employed at anydesired time and, which has a smooth thrust decay has long been soughtafter.

Accordingly, it is the principal object of this invention to provide anapparatus for motor thrust termination for use in small missiles such'asrockets which can be employed at any desired time and which has a smooththrust decay.

It is a particular object of this invention to provide such an apparatusfor use in field artillery rockets.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWING These andother objects and attendant advantages of this invention will becomemore readily understood and apparent by reference to the followingdetailed description, of which the accompanying drawing forms anintegral part. In the drawing:

FIG. 1 is a sectional view of the preferred embodiment of a tandemsolid-hybrid rocket motor of this invention;

FIG. 2 is a block diagram of the oxidizer valve control system used inthe rocket motor of FIG. 1;

FIG. 3 is a sectional view taken along line 3-3 of FIG. 1 (drawn to asmaller scale); and,

FIG. 4 is a sectional view taken along line 4-4 of FIG. 1 (drawn to asmaller scale).

DESCRIPTION OF THE PREFERRED EMBODIMENT Accurate missile range zoningmay be provided by employing a rocket having a single-chamber motorcontaining both a hybrid fuel charge and a solid propellant charge.Referring now to FIG. 1, a rocket includes a motor case 11 mountedtherein in a conventional manner. Motor case 11 has a cylindricalchamber therein with a solid propellant charge 14 in the aft end ofchamber 15 and a hybrid fuel charge 12 in the forward end of chamber 15.An exhaust nozzle 18 is mounted at the aft end of motor case 11 in-aconventional manner. A baffle gasmixer plate 16.is mounted in chamber 15so as to separate charges 12 and l4. 18 holes are drilled in mixer plate16 in a configuration illustrated in FIG. 4 with each hole containing anannular carbon insert 19 (to prevent erosion) having an orifice 41therein. Orifices 41 are positioned behind the hybrid grain spokes toproduce two turns of the gas path. Located adjacent to mixer plate 16and mounted in a conventional manner in the internal perforation ofsolid propellant charge 14 is a conventional squib igniter 8 forigniting charge 14. I

An oxidizer storage and control system is associated with hybrid fuelcharge 12 and is housed in the forward end of rocket 10. This systemincludes a combination oxidizer injector and motor head (hereinafterreferred to as injector head 26). As shown in FIG. 3, injector head 26uses thirteen modified commercial spray nozzles to provide a uniformspray pattern. Nozzles 27 discharge each of 12 spaces between grainspokes and one nozzle 29 sprays down the center of charge 12. Fullconespray patterns are used because smoother combustion is obtained thanwith hollow cone injectors. As shown in FIG. 1, a motor potentiometerpressure gauge 38 is in communication with chamber 15 via an inclinedpassageway 35 in injector head 26 (see FIG. 3) via a fitting 37 and aconduit 39.

The oxidizer storage and control system further includes a cavitatingventuri 24, in communication with nozzles 27 and 29, for flow controland measurement. An explosively-actuated oxidizer balanced poppet valve9 is actuated to an open position by squib 22 for communicating oxidizerto cavitating venturi 24 and by squib 23 for cutting off the flow ofoxidizer to cavitating venturi 24. The location of cavitating venturi 24near injector head 26 minimizes the line filling time after explosivelyactuated oxidizer valve 9 is opened. This gives more rapid motorresponse to the signal for hybrid motor ignition. A burst diaphragm 30allows an oxidizer tank 28 (which tank defines an oxidizer chamber 21)to be handled and filled as a separate unit. A suitable liquid oxidizeris contained in oxidizer chamber 21. The oxidizer in chamber 21 iscaused to burst diaphragm 30 by means of an expulsion device, in thiscase a piston 20. Piston 20 is pressurized by hot gases inside chamber33. The hot gases are introduced into chamber 33 from a conventional hotgas generator 34 mounted in closure 32. A hot gas relief valve 36,illustrated only schematically, is used for regulating the maximumpressure to be maintained in chamber 33. Viton O-rings (not shown) areused throughout the piston expulsion system to provide seals whereneeded.

Referring to FIG. 2, the output of potentiometer pressure gauge 38 isintegrated electronically by a pressure integrator 40 which connects avoltage source 42 with oxidizer valve 9 and fires it by squib 22 when apredetermined pressure-time integral is reached. This is easilyaccomplished by means of a capacitance circuit.

Before the actual operation of the tandem motor of FIG. 1 commences, hotgas generator 34 is pressurized and ready to go upon the opening ofoxidizer valve 9.

In operation, squib igniter 8 is ignited by conventional means. Solidpropellant charge 14 starts to burn and provides combustion gases which,for the most part, exit from rocket 10 through exhaust nozzle 18. A verysmall part of these gases flow toward the front of rocket 10, and thesurface of hybrid propellant charge 12 is heated by radiation andconvection. Thus, these solid propellant combustion gases heat thesurface of hybrid charge 12 sufficiently to cause ignition with theliquid oxidizer when the liquid oxidizer is later injected into hybridcharge 12. The space evacuated by solid propellant charge 14 as it burnswill later serve as a mixing chamber for more efficient hybrid fuelcharge 12 combustion. Mixer plate 16 separating charges 12 and 14provides additional mixing and will later further increase thecombustion efficiency of hybrid fuel charge 12.

Hybrid fuel charge 12 has now been heated sufficiently to ignite uponinjection of the liquid oxidizer. This occurs upon the opening ofoxidizer valve 9 at a preset pressure-time integral. This is effected bythe output of motor potentiometer pressure gauge 38, which is integratedelectronically to open oxidizer valve 9 at the preset pressure-timeintegral (which is adjusted to compensate for any valve delay andinjector filling delays).

Referring again to FIG. 2, the output of motor potentiometer pressuregauge 38 is integrated electronically by a pressure integrator 40 whichconnects a voltage source 42 with oxidizer valve 9 and fires it by squibmeans (not shown) when the preset pressure-time integral is reached.This is accomplished by means of a capacitance circuit. When oxidizervalve 9 is thus opened, liquid oxidizer from chamber 21 is expelled bypiston 20 from chamber 21 and bursts burst diaphragm 30. The oxidizer isfed through oxidizing valve 9 and cavitating venturi 24 through nozzles27 and 29 in injector head 26 into the previously heated hybrid fuelcharge 12. Charge 12 is ignited upon contact with the oxidizer, and thehybrid combustion products flow through holes 41 in mixer plate 16,through the space previously evacuated by solid propellant charge 14,and out exhaust nozzle 18. The piston expulsion system pressure has beenset (before actual operation of the tandem motor) at 1,200 p.s.i. toallow for pressure drops of 240 p.s.i. for cavitating venturi 24, 100p.s.i. for oxidizer valve 9 and line losses and 50 p.s.i. for injectorhead 26. The maximum pressure in chamber is 800 p.s.i.a. In order tohave constant thrust for both phases of burning, the solid boosterchamber pressure is also designed for 800 p.s.i.a.

The hybrid motor thrust is terminated either by the automatic closing ofoxidizer valve 9 by squib 23 (at a preset dialing of a conventionalstructure which is not shown) or by the complete expenditure of theoxidizer. This feature provides the missile zoning desired. lf desired,a variable control valve (rather than an on-off oxidizer valve 9 andoxidizer) may be employed to give 7 thrust modulation.

of this invention.

1 claim: 1. A rocket motor comprising: a motor case defining acombustion chamber therein;

a solid propellant charge at the aft end of said combustion chamber;

a solid hybrid fuel charge at the forward end of said combustionchamber, said solid propellant charge and said solid hybrid fuel chargebeing juxtaposed in tandem;

an oxidizer in fluid communication with said solid hybrid fuel charge;

means for controlling the flow of said oxidizer to said solid hybridfuel charge;

a perforated gas mixer baffle plate located intermediate adjacent endsof said solid propellant charge and said solid hybrid fuel charge toseparate said solid propellant charge from said solid hybrid fuel chargeand provide additional mixing of exhaust gases from combustion of saidsolid hybrid fuel charge as the exhaust gases pass through saidperforated baffle plate to thereby further increase the combustionefficiency of said solid hybrid fuel charge with said oxidizer;

and means for igniting said solid propellant charge.

2. The rocket motor as set forth in claim 1 wherein said gas mixerbaffle plate comprises annular carbon inserts located in holes therein,said carbon inserts defining orifices therein.

3. The rocket motor as set forth in claim 1 wherein said means forcontrolling the flow of said oxidizer to said hybrid fuel chargecomprise pressure-time integral means for timing said flow of saidoxidizer to said hybrid fuel charge.

4. The rocket motor as set forth in claim 1 wherein said hybrid fuelcharge is in the form of a wagonwheel configuration defining hybridgrain spokes, and wherein injector means for injecting said oxidizer arepositioned for injecting said oxidizer down the center of saidwagonwheel and intermediate said grain spokes.

5.-The rocket motor as set forth in claim 4 wherein said orifices insaid gas mixer baffle plate are in alignment with said hybrid grainspokes.

6. The rocket motor as set forth in claim 5 wherein said orifices arepositioned in said gas mixer baffle plate with even-numbered ones ofsaid spokes having one orifice in alignment therewith, and odd-numberedones of said spokes having'two orifices in alignment therewith.

7. The rocket motor as set forth in claim 6 wherein said spokes numbertwelve.

8. The rocket motor as set forth in claim 4 wherein :said means forcontrolling the flow of said oxidizer to :said hybrid fuel furtherincludes an explosively actuated oxidizer inlet valve located in fluidcommunication intermediate said oxidizer and said injector means.

9. The rocket motor as set forth in claim 8 wherein a cavitating venturiis located in fluid communication intermediate said inlet valve and saidinjector means, said cavitating venturi being located near said injectorhead.

1. A rocket motor comprising: a motor case defining a combustion chambertherein; a solid propellant charge at the aft end of said combustionchamber; a solid hybrid fuel charge at the forward end of saidcombustion chamber, said solid propellant charge and said solid hybridfuel charge being juxtaposed in tandem; an oxidizer in fluidcommunication with said solid hybrid fuel charge; means for controllingthe flow of said oxidizer to said solid hybrid fuel charge; a perforatedgas mixer baffle plate located intermediate adjacent ends of said solidpropellant charge and said solid hybrid fuel charge to separate saidsolid propellant charge from said solid hybrid fuel charge and provideadditional mixing of exhaust gases from combustion of said solid hybridfuel charge as the exhaust gases pasS through said perforated baffleplate to thereby further increase the combustion efficiency of saidsolid hybrid fuel charge with said oxidizer; and means for igniting saidsolid propellant charge.
 2. The rocket motor as set forth in claim 1wherein said gas mixer baffle plate comprises annular carbon insertslocated in holes therein, said carbon inserts defining orifices therein.3. The rocket motor as set forth in claim 1 wherein said means forcontrolling the flow of said oxidizer to said hybrid fuel chargecomprise pressure-time integral means for timing said flow of saidoxidizer to said hybrid fuel charge.
 4. The rocket motor as set forth inclaim 1 wherein said hybrid fuel charge is in the form of a wagonwheelconfiguration defining hybrid grain spokes, and wherein injector meansfor injecting said oxidizer are positioned for injecting said oxidizerdown the center of said wagonwheel and intermediate said grain spokes.5. The rocket motor as set forth in claim 4 wherein said orifices insaid gas mixer baffle plate are in alignment with said hybrid grainspokes.
 6. The rocket motor as set forth in claim 5 wherein saidorifices are positioned in said gas mixer baffle plate witheven-numbered ones of said spokes having one orifice in alignmenttherewith, and odd-numbered ones of said spokes having two orifices inalignment therewith.
 7. The rocket motor as set forth in claim 6 whereinsaid spokes number twelve.
 8. The rocket motor as set forth in claim 4wherein said means for controlling the flow of said oxidizer to saidhybrid fuel further includes an explosively actuated oxidizer inletvalve located in fluid communication intermediate said oxidizer and saidinjector means.
 9. The rocket motor as set forth in claim 8 wherein acavitating venturi is located in fluid communication intermediate saidinlet valve and said injector means, said cavitating venturi beinglocated near said injector head.